This invention is generally directed to liquid toner compositions and more specifically to liquid toner compositions having incorporated therein, or thereon specific charge control additives. In one embodiment of the present invention there are provided liquid toner compositions containing therein, or thereon as charge enhancing additives complexes of amino acids and polyvalent metals as more specifically illustrated hereinafter. Another important embodiment of the present invention resides in improved liquid toner compositions useful in electrostatic printers and plotters, commercially available from Versatec, Inc. for example, which toner compositions are comprised of liquid media or liquid carriers, resin binders, pigment particles, and charge control additives selected from complexes of polyvalent metal compounds with amino acids, which additives are preferably present as a coating on the pigment particles. The aforementioned toner compositions possess a number of important characteristics inclusive of stable electrical properties, and wherein the charge additives selected are insoluble in the solvents and liquid vehicles selected for the toners; and moreover the liquid toners of the present invention enable final developed prints with excellent quality, that is substantially no background deposits, high density, and excellent solid area coverage. Accordingly, the particles in the liquid developer compositions of the present invention are positively charged, which charge is substantially stable for extended time periods, that is for example it does not usually decrease or increase with use; and moreover, the toner particles have excellent suspension properties, that is there is not tendency for such particles to settle or form agglomerates. Additionally, the toner compositions of the present invention possesses many of the characteristics mentioned herein at high printing speeds, that is up to two inches per second as well as low speeds such as 0.05 inch per second. Furthermore, the toner compositions of the present invention are useful in electrophotographic imaging apparatus, and more particularly the toners of the present invention can be selected for obtaining images of excellent quality in electrostatic plotters, inclusive of those commercially available from Versatec, Inc. Further, the liquid tones of the present invention may be selected for the development of images in various other systems, inclusive of xerographic processes, electrostatic printing, and facsimile systems; color proofing processes; and the like.
Development of electrostatic latent images with liquid developer compositions comprised of, for example, a dispersion of pigments in a liquid hydrocarbon are known. In these methods, the electrostatic latent image, which is usually formulated on a photoconductive member, is transported through a bath of the aforementioned liquid developer. Contact with the liquid developer causes the charged pigment particles present therein to migrate through the liquid to the photoreceptor surface in the configuration of a charged image. Thereafter, the toner electrostatic image is electrostatically transferred from the photoconductor surface to plain paper.
There are disclosed in U.S. Pat. No. 3,554,946 liquid developers for electrophotography comprised of a carrier liquid consisting of a hydrocarbon, negatively electrostatically charged toner particles dispersed in the carrier liquid, and a pigment therein such as carbon black, aniline black, prussian blue, phthalocyanine red, and cadmium yellow. In accordance with the teachings of this patent, a copolymer is coated on the surface of the pigment particles for the primary purpose of imparting a negative electrostatic charge to these particles. Other patents disclosing similar liquid developer compositions includes U.S. Pat. Nos. 3,623,986; 3,625,897; 3,900,412; 3,976,583; 4,081,391 and 3,900,412. In the '412 patent, there is disclosed a stable developer comprised of a polymer core with a steric barrier attached to the surface of the polymer selected. In column 15 of this patent, there are disclosed colored liquid developers by selecting pigments or dyes, and physically dispersing them by ball milling or high shear mixing.
Additionally, there is described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
In addition, there are illustrated in British Patent Publication No. 2,169,416, the disclosure of which is totally incorporated herein by reference, liquid developer compositions comprising toner particles associated with a pigment dispersed in a nonpolar liquid, and wherein the toner particles are formulated with a plurality of fibers or tendrils from a thermoplastic polymer, and carry a charge of polarity opposite to the polarity of the latent image. These toners permit in some instances excellent transfer efficiencies, however, they are apparently difficult to prepare.
Representative prior art patents primarily of background interest are U.S. Pat. Nos. 4,306,009; 4,363,863; 4,374,918 and 4,521,505. The main disadvantage associated with the aforementioned prior art inks resides in the release or evaporation of the vehicle selected, such as Isopar since these toners are prepared in a manner that does not result in the entrapment of the vehicle.
Also, there are described in U.S. Pat. No. 4,014,856 liquid toners comprising carrier liquids and toner particles wherein the carrier liquid comprises a bivalent or trivalent metal salt of an oxyacid derived from phosphorus containing at least one organic residue, and one or more members selected from the group consisting of amines, polyurethanes, and alkylated polymers of a heterocyclic N-vinyl monomer wherein the polarity of the toner material is controlled for the purpose of obtaining optimum image density and contrast, reference the abstract of the disclosure. It is further indicated in this patent that when carbon blacks are used as the toner material it is possible to control the polarity to obtain either positive or negative working toner compositions. Specific embodiments of the invention of the '856 patent are outlined in column 2, beginning at line 34, and continuing on to column 3. Examples of components selected for the toners of this patent are described in column 4. This patent, however, is silent with respect to liquid toner compositions which contain therein the specific charge control additives of the present invention, and which enable some of the advantages achievable with such charge control additives.
Disclosed in U.S. Pat. No. 3,844,966 are electrostatic liquid toner compositions comprised of a carrier liquid with toner particles suspended therein, and also containing a trivalent or tetravalent metal salt of an organic acid plus an organic amine dissolved in the carrier, reference the Abstract, and column 1, lines 56 to 64. Examples of suitable metal salts selected for the toner of this patent are outlined in column 2, beginning at line 22, and include trivalent and tetravalent cation salts of aluminum, iron, salts of organic acids, and the like. Second additive examples include any organic amine, such as ammonia, and other materials including organic acid esters, reference column 2, lines 32 to 64.
In addition, there are illustrated in German Published Application No. 3,529,780 liquid electrostatic developers containing charge regulators therein which are formulated by reacting an amino acid in an organic solvent with a titanium compound, and mixing and reacting the reaction mixture with an amount of water at least equimolar to the titanium compound, reference the Derwent abstract, a copy of which is being submitted with the mailing of this application to the U.S. Patent Office. Examples of preferred components selected are outlined in the abstract, and moreover it is indicated that the liquid developer enables excellent unblurred copies of high quality.
Furthermore, there are illustrated in copending application U.S. Ser. No. 846,164, the disclosure of which is totally incorporated herein by reference, stable black liquid developers comprised of an insulating liquid medium having dispersed therein black marking particles comprised of a thermoplastic resin core which is substantially insoluble in the dispersion medium, and chemically or physically anchored to the resin core an amphipathic block or graft copolymer steric stabilizer which is soluble in the dispersion medium; and wherein dyes comprised of a specific mixture are imbibed in the thermoplastic resin core with the mixture of dyes being dispersible at the molecular level, and therefore soluble in the thermoplastic resin core and insoluble in the dispersion medium. Furthermore, in U.S. Pat. No. 4,762,764, the disclosure of which is totally incorporated herein by reference, there is illustrated dyed sterically stabilized polymer particle for incorporation into negatively charged electrophoretic liquid developers.
Although the above described liquid toners are suitable for their intended purposes, there remains a need for improved ink compositions. There also is a need for ink compositions with stable electrical properties, and wherein the charge enhancing additive is permanently associated with the toner composition. Additionally, there is a need for liquid inks, or toner compositions wherein there are selected certain charge control additives thereby enabling such compositions to possess stable electrical properties for extended time periods. Moreover, there is a need for positively charged liquid toner compositions wherein the charge control additives are present as a coating on the pigment particles. Further, there remains a need for liquid toner compositions with complexes of amino acids with polyvalent metals as charge control components, which additives are insoluble in the liquid carrier and are substantially insulating and not conductive in comparison to prior art charge control materials. In this regard, most known charge control agents are soluble in the carrier, and they are also conductive. Toners containing soluble charge control agents usually have resistivity lower than 10.sup.9 ohm-cm, whereas the toners of the present invention, which contain insoluble charge control agents, usually have a higher resistivity of greater than 10.sup.10 ohm-cm. There is also a need for toner compositions wherein the charge enhancing additive is insoluble in the solvents utilized thus enabling the resulting compositions to possess desirable characteristics as mentioned herein, including the formulation of developed images of excellent quality of high density, and low background deposits. Additionally, there is a need for liquid toner compositions wherein the charge control additive selected is insoluble in the carrier liquid thus enabling, for example, toners with relatively high resistivities, that is greater than 10.sup.10 ohm-cm as contrasted, for example, to some of the prior art liquid toners wherein the charge control agents are soluble in the carrier vehicle, and there results toners with resistivities of lower than 10.sup.9 ohm-cm.